The invention relates to devices and to systems and to methods for remote or non-contact temperature measurement. Such devices are known in temperature measurement art as radiometers or as pyrometers or infrared cameras. They comprise a detector for receiving infra red heat radiation emanating from an energy zone on the surface of an object of measurement, an infra red (IR) optical system for imaging the heat radiation emanating from the energy zone onto the detector; and a sighting system for identifying the position and size of the energy zone on the surface of the object of measurement by visible light display. A further processing means associated with the detector converts the detector signal into a temperature indication and may also produce a temperature display upon the radiometer. The method of the invention includes the steps of measuring the distance between the radiometer and the target surface; and converting the measured distance by a calculation in the radiometer into a value, which represents the size of the radiometer optical field of view, and which is used to identify the extent of the energy zone which may also be displayed.
An IR optical sub-system is designed so that at a particular distance between the radiometer and the target surface, for the most part, heat from a known and identified area of the surface of the object of measurement, namely, the energy zone, is focused onto the detector. In the usual case the term energy zone is defined as the area from which about 90% of the heat rays focused onto the detector are emitted. In other cases the amount may be between about 50% and a value up to 100% of the heat.
The pattern of the dependence of the size of the energy zone upon the measurement distance depends upon the design of the IR optical system. There is a recognized relation between the measured distance from the radiometer to the energy zone on the surface of measurement and the respective size of the optical field of view of the radiometer. The measurement of distance is used to calculate the size of the optical field of view. Focus may be done manually or by a known auto-focus means.
In non-contact temperature measurement methods under practical conditions, the energy zone on the surface of the object to be examined should be made visible to the device operator in a suitable way, i.e., by a sighting system. For example, in U.S. Pat. No. 5,368,392 various light projection sighting methods of outlining the energy zone using laser beams are described. Such methods include: use of a laser beam to identify the center of the energy zone and/or use of a beam splitter to produce from a single laser several separate static laser beams which may surround the energy zone with multiple illuminated static points of light; and also include use of a single moving or dynamic laser beam to circumscribe the zone. Multiple separate lasers may be used to produce separate sighting beams.